1. Field of the Invention
This invention relates to a route setting device and method, and especially to a route setting device and method for setting a destination route which is a route form a departure point to a set destination (target point), and a navigation system for performing route guidance concerning the destination route being set by the route setting device.
2. Related Art
There has been known a navigation system, which detects a present position changing as a vehicle travels by using GPS (Global Positioning System) or the like, displays the present position on a display unit with a road map, and performs a route guidance by setting an adequate route from the present position to a destination. Such a navigation system contributes smoother driving. As such a route setting, Dijkstra's algorithm or conformable method is used in general. Concretely, the route is set by the following steps. A route calculation cost (estimated value for each route) from a present position to each node is calculated by using a link connection data for a link between the nodes. After all of the cost calculations to the destination are completed, specific links are connected each other so that a total cost becomes minimum. A continuous link formed by connecting specific links is determined as the set destination route.
Here, because the route is continuous to the destination, roads into which a vehicle cannot enter such as one-way road or pedestrian-only road cannot be adopted as a part of the route. Therefore, when such a traffic regulation is detected from link connection data, the destination route is determined without using the road having such the traffic regulation.
By the way, not all the traffic regulations do not always uniformly regulate traffics of all the vehicles such as the above-described one-way road or pedestrian-only road. For example, freeways in metropolis of USA have a carpool lane system as the traffic regulation. Carpool lanes are provided for the purpose of recommending carpooling (riding together) to decrease the number of vehicles traveling the freeways. Concretely, the vehicle is allowed to travel the carpool lane when plural passengers are riding together thereon, and is regulated (prohibited) when the passenger is only one (only driver).
Here, some carpool lanes are defined by partitioning one of plural lanes by a lane defining line (or center line) or by a guardrail as shown in FIG. 10A, and some carpool lanes are provided independently from normal lanes (main lanes) as shown in FIG. 10B. Some carpool lanes change the traffic regulation based on time, month or season. When the driver makes a violation of the regulation, the driver is punished. However, some of such the carpool lanes are provided to have some advantages compared to the normal lanes. That is, the regulation described the above causes decreasing the number of vehicles traveling the carpool lanes so that the vehicles tend not to stuck a traffic congestion, the carpool lanes are near to exits, or route distances of the carpool lanes are shorter than those of normal lanes.
However, according to the conventional route setting device, the carpool lanes are substantially eliminated from consideration of the destination route setting by treating them as closed roads at all times or setting the route calculation cost very high at all times. In other words, since the traffic regulation of the carpool lane is so indefinite that the vehicle can not travel the carpool lane when the passenger is only one but can travel when the passenger is plural, the carpool lanes are substantially eliminated from consideration of the destination route setting in order to comply with even when the passenger is only one. Therefore, even when the vehicle complies with the condition that can travel the carpool lanes, that is, plural passengers are riding on the vehicle, a detour is set as the set destination route although a destination route including the carpool lanes is actually the nearest route, because the carpool lanes are eliminated from consideration.
The traffic regulation has explained by using the carpool lane, however, the other traffic regulations also exist. For example, there is a route that includes a tunnel through which only low-height vehicle whose height is lower than a predetermined value can pass or a route through which a large size vehicle cannot pass but a small size vehicle can pass. In this situation, too, all vehicles have to be uniformly regulated (prohibited) to travel. Therefore, the best destination route cannot be set for the vehicle actually permitted to travel such the lanes or roads.
In other words, the conventional route setting is based on only road-side data (e.g., link data or link connection data) but is not based on a condition of vehicle side.